A reaction of phenols with formaldehyde in the presence of an acidic catalyst is generally known as a reaction for producing a phenol-novolac resin or the like. On the other hand, it has also been shown that a reaction with aldehydes such as acetoaldehyde, propionaldehyde, isobutyraldehyde, crotonaldehyde, and benzaldehyde produces polyphenols (see Patent Literature 1) and a novolac resin (see Patent Literature 2). In addition, it has also been shown that a reaction with hydroxybenzaldehyde having both properties of phenol and aldehyde can produce a novolac-type resin (see Patent Literature 3).
While the polyphenols and the novolac resin are used as a coating agent for a semiconductor and a resist resin, they are required for having heat resistance as one of properties in such applications.
On the other hand, as a composition for forming an antireflective film useful for microfabrication in a lithography process and suitable for manufacturing in particular an integrated circuit element, known is a composition for forming an antireflective film, containing a polymer (acenaphthene resin) having a structure represented by the following formula as a monomer unit, and a solvent (see Patent Literature 4).
[wherein R1 denotes a monovalent atom or group, n is an integer of 0 to 4, R2 to R5 independently denote a hydroxy group, or a monovalent atom or group.]
However, this technique in Patent Literature 4 has difficulties in that materials are expensive, the reaction conditions for obtaining the acenaphthene resin are stringent, and there are a large number of reaction steps and the reaction is complicate.
On the other hand, semiconductor devices are manufactured through microfabrication by lithography using a photoresist material, but are required to be made finer by a pattern rule in accordance with the increase in integration degree and the increase in speed of LSI in recent years. In lithography using light exposure, which is currently used as a general-purpose technique, the resolution is now approaching the intrinsic limitation associated with the wavelength of the light source.
A light source for lithography, for use in forming a resist pattern, has a shorter wavelength from a KrF excimer laser (248 nm) to an ArF excimer laser (193 nm). However, as the resist pattern is made finer and finer, there arise a problem of resolution and a problem of collapse of the resist pattern after development, and therefore there is demanded for making a resist film thinner. On the other hand, if the resist film is merely made thinner, it is difficult to achieve the resist pattern having a film thickness sufficient for processing a substrate. Accordingly, there is increasingly required a process in which not only the resist pattern but also a resist underlayer film is prepared between a resist and a semiconductor substrate to be processed and the resist underlayer film is allowed to have a function as a mask at the time of processing the substrate.
Currently, as the resist underlayer film for such a process, various ones are known. For example, in order to provide a resist underlayer film for lithography, having a selection ratio of dry etching rate close to the resist, unlike a conventional resist underlayer film having a high etching rate, there has been proposed a material for forming an underlayer film for multilayer resist process, containing a resin component having at least a substituent which releases a terminal group to form a sulfonic acid residue when a predetermined energy is applied, and a solvent (see Patent Literature 5). In addition, in order to provide a resist underlayer film for lithography, having a smaller selection ratio of dry etching rate than the resist, there has been proposed a resist underlayer film material including a polymer having a specified repeating unit (see Patent Literature 6). Furthermore, in order to provide a resist underlayer film for lithography, having a smaller selection ratio of dry etching rate than the semiconductor substrate, there has been proposed a resist underlayer film material including a polymer formed by co-polymerizing a repeating unit of acenaphthylene, and a substituted or non-substituted repeating unit having a hydroxy group (see Patent Literature 7).
On the other hand, as a material for allowing such a resist underlayer film to have a high etching resistance, an amorphous carbon underlayer film is known, which is formed by CVD using methane gas, ethane gas, acetylene gas, or the like as a raw material. However, there is demanded, in terms of process, a resist underlayer film material that can form a resist underlayer film in a wet process such as a spin coating method or screen printing.
In addition, as a material that is excellent in optical characteristics and etching resistance and that is capable of being dissolved in a solvent and being applied to a wet process, the present inventors have proposed a composition for forming an underlayer film for lithography, which contains a naphthalene formaldehyde polymer including a specified constituent unit, and an organic solvent (see Patent Literature 8). However, the technique in Patent Literature 8 is demanded to be improved in terms of etching resistance.